Complex effects of landscape, habitat and reservoir operation on riparian vegetation across multiple scales in a human-dominated landscape

Riparian ecosystems associated with dam reservoirs, are subjected to a wide variety of stressors that alter their plant community composition and diversity patterns and affect riparian ecosystem services delivery. To enhance riverine and regional ecosystem management, the different influences of dam-induced environmental change and anthropogenic factors within and around the reservoir need to be understood across multiple scales. To elucidate the relative importance of these factors, this study examines riparian vegetation composition and structure along the Three Gorges Reservoir (China) and their responses to surrounding landscapes, habitat quality and reservoir management (three groups of influences). We recorded vegetation data in 5 × 1 m quadrats embedded in three stratified elevational zones 145-155 m, 155-165 m, and 165-175 m. Correspondence analyses were used to partition the contribution of various influences in explaining vegetation patterns at three organisational scales: site, community and individual species. Vascular plants totaled 150 species in 130 genera from 56 families. Overall, vegetation responses were idiosyncratic across the analysed scales. At the site-scale, landscape was most important in structuring communities. However, localised habitat and reservoir flooding influences have higher explanatory power at the community-scale, regardless of elevational divergence. Overall, there seem to be a general trend in the importance of variables across all analysed scales. Among the landscape factors, variables based on a landscape gradient model were much more influential than those based on the conventional patch mosaic model. Given the heavily inter-correlated nature of many variables at varying scales of human altered landscapes, the best way forward for reservoir riparian vegetation management strategies is to develop multi-scale, synthetic and location-specific approaches that may optimise conservation efforts.